Reference · Printable
Scale ruler
An architect’s scale rule reads real-world distances straight off a scaled drawing. Choose the scale your drawing was made at — 1:50 and 1:100 cover most metric work, 1/4" = 1'-0" most US floor plans — print at 100%, and measure without doing any arithmetic.
Metric ratios — which scale for what
The third column is the practical test: how much paper one real metre occupies. Below about 2 mm per metre the drawing stops being measurable by hand and becomes a location reference instead.
| Scale | Typically used for | 1 metre on paper |
|---|---|---|
| 1:5 | Joinery and component details, furniture drawings | 200 mm |
| 1:10 | Large construction details, fittings and assemblies | 100 mm |
| 1:20 | Construction details, joinery, stair sections | 50 mm |
| 1:25 | Detailed room plans, kitchen and bathroom layouts | 40 mm |
| 1:50 | Floor plans, sections and elevations — the everyday architectural scale | 20 mm |
| 1:100 | Whole-building plans, apartment layouts, planning submissions | 10 mm |
| 1:200 | Large buildings, schools and hospitals on a single sheet | 5 mm |
| 1:500 | Site plans and building footprints in their plot | 2 mm |
| 1:1000 | Site location plans, small masterplans | 1 mm |
| 1:1250 | Location plans for planning applications (UK convention) | 0.8 mm |
| 1:2500 | Large site and land-registry plans | 0.4 mm |
US architectural and engineer scales
A US drawing states its scale as a fraction of an inch standing for one foot rather than as a ratio, and the two sets are not interchangeable: architectural scales divide the foot into inches, engineer scales divide it into tenths. Both are in the generator, labelled in feet — a plan drawn at 1/4" = 1'-0" is dimensioned in feet and inches, so printing metres on the rule would be arithmetically correct and professionally useless.
| Scale | Ratio | Typically used for | 1 foot on paper |
|---|---|---|---|
| Architectural | |||
| 3" = 1'-0" | 1:4 | Full-size details and joinery | 76.2 mm |
| 1-1/2" = 1'-0" | 1:8 | Construction details | 38.1 mm |
| 1" = 1'-0" | 1:12 | Millwork and cabinetry | 25.4 mm |
| 3/4" = 1'-0" | 1:16 | Wall sections | 19.1 mm |
| 1/2" = 1'-0" | 1:24 | Enlarged plans, kitchens and baths | 12.7 mm |
| 3/8" = 1'-0" | 1:32 | Small building plans | 9.53 mm |
| 1/4" = 1'-0" | 1:48 | The standard residential floor plan | 6.35 mm |
| 3/16" = 1'-0" | 1:64 | Larger floor plans | 4.76 mm |
| 1/8" = 1'-0" | 1:96 | Whole-building plans and elevations | 3.18 mm |
| 1/16" = 1'-0" | 1:192 | Large buildings, key plans | 1.59 mm |
| Engineer | |||
| 1" = 10' | 1:120 | Detailed site plans | 2.54 mm |
| 1" = 20' | 1:240 | Site and grading plans | 1.27 mm |
| 1" = 30' | 1:360 | Site layouts | 0.85 mm |
| 1" = 40' | 1:480 | Larger sites | 0.64 mm |
| 1" = 50' | 1:600 | Subdivision and utility plans | 0.51 mm |
| 1" = 100' | 1:1200 | Overall site and location plans | 0.25 mm |
The ratio column is what CAD viewports and print dialogs ask for. It follows from the fraction: a quarter inch of paper per twelve inches of building is 12 ÷ 0.25, or 1:48.
Why the ratio is written that way
“1:50” means one unit on the drawing stands for fifty of the same unit in reality — the units cancel, which is why the notation carries no millimetres or inches and works identically for a plan printed in Athens or Auckland. It also means the ratio is only true while the drawing keeps its printed size. Rescale the sheet and the ratio silently changes with it, which is the single most common source of wrong measurements taken off a printed plan.
The same logic drives the scaling percentages in our paper size converter: moving an A3 drawing onto A4 at 71% turns a 1:50 drawing into a 1:70.7 drawing. If you must reduce a drawing, note the new ratio on the sheet — or print a matching scale ruler and staple it to the drawing.
Frequently asked questions
What does a scale ruler actually do?
It removes the arithmetic. On a 1:50 drawing, a wall measuring 20 mm on paper is one metre in reality — a scale rule has that conversion built into its markings, so you read "1 m" directly instead of measuring 20 mm and dividing. Each face of a physical scale rule carries a different ratio; here you print the one you need.
Which scale should I use for a floor plan?
1:50 for a room or apartment you want to see in detail, 1:100 for a whole house or a planning drawing that must fit one sheet. The rule of thumb is that 1:50 shows door swings and furniture comfortably, while 1:100 shows the building shape and room relationships. Below that, 1:200 and 1:500 are for the building in its site rather than the rooms inside it.
How do I read a scale ruler?
Line the zero mark up with one end of what you are measuring and read the number at the other end — that number is already in real-world metres. The small divisions between the numbered marks subdivide the metre, typically into tenths, so a reading between 3 and 4 with two small marks past 3 is 3.2 m.
Why does print accuracy matter more for a scale ruler?
Because the error multiplies. If your printer shrinks the page by 3%, a life-size ruler is visibly wrong the moment you hold a real ruler against it. A 1:100 scale ruler with the same 3% error looks perfectly normal and silently reports every distance 3% short — 30 centimetres of real building for every 10 metres measured. Print at 100% / Actual size and check against a known ruler first.
Does the drawing itself have to be printed at the right scale?
Yes, and this is the mistake that catches people out. A 1:50 drawing printed "fit to page" on A4 when it was drawn for A3 is no longer at 1:50, and no scale rule can save it — the printed drawing is at some arbitrary ratio. Check the drawing has a printed scale bar and measure it before trusting any dimension you take off the sheet.
Are imperial scales supported?
Yes. The generator carries the full US set: ten architectural scales from 3" = 1'-0" down to 1/16" = 1'-0", and six engineer scales from 1" = 10' to 1" = 100'. They are labelled in feet rather than metres, because that is how the drawings are dimensioned, and the foot is subdivided into inches wherever the printed spacing leaves room to read them. The life-size setting prints inches down to sixteenths.
What ratio is 1/4 inch scale?
1:48. A quarter inch of paper stands for one foot of building, and a foot is twelve inches, so 12 ÷ 0.25 = 48. The same arithmetic gives 1/8" = 1'-0" as 1:96 and 1/2" = 1'-0" as 1:24. Engineer scales are more direct: 1" = 20' is 240 inches per inch, or 1:240. You need the ratio rather than the fraction whenever you set a CAD viewport or a print scale.
What is the difference between an architect scale and an engineer scale?
What they divide the foot into. An architect scale splits it into inches, because a building is dimensioned in feet and inches — so 1/4" = 1'-0" is read as 12'-6". An engineer scale splits it into tenths, because survey and civil work is dimensioned in decimal feet — 1" = 20' is read as 12.5'. Using the wrong rule on a drawing gives a plausible number that is wrong, which is why a set of drawings names the scale on every sheet.